Catheters for drug infusion and fluid aspiration are well known. Such catheters are frequently positioned within the vascular system of a patient for long term therapy, e.g., the administration of saline, nutrients, medication, etc.
However, one problem commonly associated with the use of catheters, particularly when left in position for an extended length of time, is that clotting or thrombosis commonly occurs around the distal opening of the catheter lumen. Although this effect is most pronounced when such catheters are used for aspiration, it is not unknown for thrombosis to occur at the distal opening of a catheter utilized for infusion due to the effects of retrograde blood flow into the catheter. Thus, it is possible for a thrombosis to substantially or even completely obstruct fluid flow through the catheter over an extended period of time, thereby posing a potentially life threatening risk for the patient.
Further, it is also possible for a clot or thrombus to form at the distal end of a catheter and then break loose from the catheter and flow through the vascular system to a point where the thrombus comes to rest within a portion of the vascular system wherein the diameter of the vessel is less than the diameter of the thrombus. As such, it will be appreciated that the thrombus necessarily impedes further flow of blood through the vessel. Such breaking loose of thrombus from the catheter is commonly caused by flushing of the catheter in an attempt to mitigate the effects of thrombus upon fluid flow through the catheter lumen.
As will be appreciated, if a thrombus breaks loose from the catheter and subsequently obstructs a blood vessel of a critical organ such as the brain, heart, or lung, the results of such blockage may potentially be very serious, possibly even fatal. Stroke, heart attack, and pulmonary embolism have been known to result from such blockage.
In an attempt to prevent the retrograde fluid flow which causes such thrombosis, contemporary practice is to utilize a closed end catheter having a single, longitudinally extending, slit valve disposed near the distal end thereof. The slit tends to close when fluid is not flowing therethrough, thereby mitigating retrograde fluid flow.
Such slit valves, when formed in the convex circular wall of a catheter, are subject to a keystone effect, wherein the slit easily facilitates infusion by spreading open when the fluid pressure within the catheter is increased, i.e., greater than that outside thereof, but does not readily facilitate aspiration when the fluid pressure within the catheter is reduced, i.e., lower than that outside thereof. More particularly, when the fluid pressure inside of the catheter is slightly lower than that outside thereof, the two sides of the slit valve tend to be urged even tighter together. A substantially lower pressure is thus required within the catheter as compared to that outside thereof in order to force the two sides of the slit valve to bend sufficiently inward so as to effect substantial opening of the slit. The slit valve therefore requires a substantially greater pressure differential to effect aspiration than it does to effect infusion. Thus, as will be appreciated by those skilled in the art, a slit valve formed in the convex surface of a circular catheter wall is much more efficient for effecting infusion than for effecting aspiration.
In an attempt to overcome the keystone effect in contemporary catheter construction, the catheter wall within which the slit valve is formed may be weakened, by treating with dimethylsiloxane, for example. Optionally, the slit valve may be formed upon a planar surface within a recess formed at the distal end of the catheter. By forming the slit upon a planar surface, a two-way slit valve is provided. Both infusion and aspiration may be performed via such a two-way slit valve. Thus, when the slit is formed upon a planar portion of the catheter, fluid flows therethrough in either direction with equal ease. Furthermore, there is no substantial difference in the pressure differential required for infusion and aspiration. One example of a catheter utilizing a slit formed upon a planar surface within a recess is disclosed in U.S. Pat. No. 5,261,885 issued to Lui on Nov. 16, 1993 and entitled VALVED CATHETER.
Additionally, slit valves may be formed without chemically weakening the walls of the catheter by utilizing lumen geometry which inherently provides weakened portions of the catheter wall which act as hinges. The hinges facilitate opening and closing of the slit valves. One example of a catheter utilizing such construction is disclosed in U.S. Pat. No. 4,753,640 issued to Nichols et al. on Jun. 28, 1988 and entitled CATHETERS AND METHODS.
However, one disadvantage of such contemporary slit valve catheters is that they tend to be inherently complex in construction, thus undesirably increasing the cost thereof. As such, although such construction does overcome the problems associated with the keystone effect, it does so at considerable cost. Additionally, such slit valve catheters are not completely immune to the effects of thrombosis, particularly when utilized for extended periods of time.
In view of the shortcomings of the prior art, it is desirable to provide a catheter which may be utilized for either infusion or aspiration without the performance or cost thereof being adversely affected by the keystone effect, and which is less prone to the undesirable effects of thrombosis than contemporary catheters.